Load sensor

ABSTRACT

The present invention relates to a load sensor comprises an annular gauge ring comprising an annular inner ring portion and an annular outer ring portion. The gauge ring has strainable beam members and flexing beam members. The beam members interconnect the ring portions. The flexing beam members are thicker in comparison to the strainable beam members so that the flexible beam members are less subject to elongation and compression due to strain in comparison to the strainable beam members such that the flexing beam members substantially limit the relative movement between the ring portions to the load measuring direction when a load with a force component in the load measuring direction is applied to one of the ring portions by (1) resisting elongation and compression to substantially prevent relative movement between the ring portions in a transverse direction and (2) flexing to allow limited relative movement between the ring portions in the load measuring direction. The strainable beam members are constructed and arranged such that the substantially isolated relative movement between the ring portions creates a strain in the load measuring direction in the strainable beam members. The strain has a magnitude directly related to a magnitude of the force component in the load measuring direction. A strain measuring an outputting device is adapted to measure the magnitude of the strain and to thereafter output the measured strain magnitude as an output signal which can be used to calculate the force component magnitude and hence the applied load. The load sensor of the present invention may be used in a variety of applications. The load sensor is particularly well suited for measuring belt tension in both idler and torque transmitting pulley assemblies. Also, the load sensor may be used to measure the co-efficient of friction between a bushing and an oscillating shaft.

[0001] The present invention relates to a load sensor and, inparticular, to a load sensor for measuring belt tension in dynamicsystems such as an idler or torque transmitting pulley.

[0002] In vehicle engines which have a number of belt driven components,proper belt tension is important to reducing belt noise, increasing beltlife, and enhancing performance. If the belt is too tense, the belt'seffective life will be reduced and increased belt noises will occurduring vehicle operation. If the belt is too slack, slippage between thebelt and its associated pulleys may occur, thereby causing a deleteriouseffect on engine performance.

[0003] A number of devices are known for measuring belt tension.Three-point tension measurement devices are crude devices which are notoften used because of two major drawbacks. First, the device is bulkyand cannot be used with tight belt drives, such as timing belt drives inautomotive engines. Second, the device considerably changes the dynamicbehavior of the belt system, and therefore does not provide accuratemeasurements.

[0004] Static and dynamic belt span vibratory frequency measurementdevices, such as clavis gauges or laser probes, measure the frequency ofa laterally vibrating belt. The measurement can thereafter be used tocalculate the actual belt tension, providing the mass of the belt andthe span end pivot conditions are known. Because these conditions arenot always constant, this method is not always accurate. Theseinaccuracy problems increase when measuring the frequency of a runningbelt, especially during mixed mode belt vibrations. Furthermore,measuring the frequency of a running belt only reveals the averagedynamic tension, not the highs and lows of the belt tension.

[0005] Belt tension can also be measured using tension-sensitivecoatings on the belt. This method, however, is highly sensitive to otherbelt stresses (e.g., belt twisting) in addition to pure tension. Also,this method is cumbersome, expensive, and unreliable in environmentallydemanding conditions such as automotive engines.

[0006] Torque sensors on driven and driving pulleys or sprockets arecommercially available devices that measure belt tension with relativelyhigh accuracy. These sensors, however, can seldom be used due to spacelimitations, especially on timing belt drives. Furthermore, their highinertia makes them unacceptable for measuring dynamic system behavior.

[0007] Custom-made strain gauged drive components may also be used tomeasure belt tension, but these are time consuming and expensive tomanufacture because of their customized nature. In addition, thesedevices are generally inaccurate due to lack of thermal compensating.Furthermore, in most cases, the strain gauged section of the device isrelatively far from the belt/pulley interface, introducing errors,especially those caused by inertia in high frequency measurementconditions. This usually results in the device itself vibrating, whichcan be witnessed as negative force readings, noise, and high hysteresisvalue readings. Finally, these types of devices are highly sensitive tobelt mistracking, i.e., belt centerline variation.

[0008] It is therefore an object of the present invention to provide apulley assembly in which dynamic belt tension can be accuratelymeasuring without affecting the dynamic behavior of the driven system.In order to achieve this object, the present invention provides a pulleyassembly for measuring driving element tension in a system driven by atensioned endless driving element. The pulley assembly comprises arotatable pulley member having a driving element engaging outer surfaceengageable with the tensioned driving element such that the drivingelement applies a load to the pulley member directly related to thedriving element tension. The load has a force component in a loadmeasuring direction. The pulley member is mounted to a shaft assemblyalso comprises a load sensor which in turn comprises an annular gaugering comprising an annular inner ring portion and an annular outer ringportion. The gauge ring is operatively associated with one of the pulleymember and the shaft such that the load applied to the pulley membercauses relative movement between the ring portions. The ring hasstrainable beam members extending in the load measuring direction andflexing beam members extending in a transverse direction generallyperpendicular to the load measuring direction. The strainable beammembers and the flexing beam members interconnect the ring portions.

[0009] The flexing beam members are thicker in comparison to thestrainable beam members so that the flexing beam members are lesssubject to elongation and compression due to strain in comparison to thestrainable beam members such that the flexing beam members substantiallylimit the relative movement between the ring portions to the loadmeasuring direction when the load is applied to the pulley member by (1)resisting elongation to substantially prevent relative movement betweenthe ring portions in the transverse direction and (2) flexing to allowlimited relative movement between the ring portions in the loadmeasuring direction. The strainable beam members are constructed andarranged such that the limited relative movement between the ringportions creates a strain in the load measuring direction in thestrainable beam members. The strain has a magnitude directly related toa magnitude of the force component in the load measuring direction. Theload sensor also comprises a strain measuring and outputting deviceoperable to measure the magnitude of the strain and to thereafter outputthe measured strain magnitude as an output signal which can be used tocalculate the force component magnitude and hence the driving elementtension.

[0010] The pulley assembly of the present invention has a number ofadvantages over tension measuring devices known heretofore. Mostimportantly, the use of the load sensor in the pulley assembly of thepresent invention does not significantly affect the dynamic behavior ofthe driven system. Therefore, it is possible to obtain accurate readingsof the belt tension as they would be found in practical applications. Inaddition, because the strainable beam members are relatively thin theyare sensitive to the applied load and the resulting measurements are notaffected by any transverse loading components because of the relativethickness of the transverse flexing beam members. Furthermore, the loadsensor in the pulley assembly of the present invention can be arrangedin close proximity to the belt/pulley interface such that slightvariations in belt tension can be sensed by the measuring and outputtingdevice. Thus, the load sensor of the present invention provides enhancedsensitivity to dynamic load changes.

[0011] The pulley assembly of the present invention can take a varietyof forms. As will be seen from the following detailed description andthe accompanying drawings, the gauge ring may be fixedly mounted to afixed shaft with the pulley member rotatably mounted to the outside ofthe gauge ring, preferably by a ball bearing assembly. Additionally, theshaft may be rotatable and the gauge ring may be fixedly mounted to theshaft with the pulley member fixedly mounted to the gauge ring such thatall three components rotate together. This arrangement can beparticularly useful not only in an idler pulley assembly but also in atorque transmitting pulley assembly.

[0012] In its broadest aspects, the present invention is concerned withthe load sensor itself out of the pulley assembly environment. The loadsensor of the present invention comprises an annular gauge ringcomprising an annular inner ring portion and an annular outer ringportion. The gauge ring has strainable beam members and flexing beammembers. The beam members interconnect the ring portions. The flexingbeam members are thicker in comparison to the strainable beam members sothat the flexible beam members are less subject to elongation andcompression due to strain in comparison to the strainable beam memberssuch that the flexing beam members substantially limit the relativemovement between the ring portions to the load measuring direction whena load with a force component in the load measuring direction is appliedto one of the ring portions by (1) resisting elongation and compressionto substantially prevent relative movement between the ring portions ina transverse direction and (2) flexing to allow limited relativemovement between the ring portions in the load measuring direction. Thestrainable beam members are constructed and arranged such that thesubstantially isolated relative movement between the ring portionscreates a strain in the load measuring direction in the strainable beammembers. The strain has a magnitude directly related to a magnitude ofthe force component in the load measuring direction. A strain measuringan outputting device is adapted to measure the magnitude of the strainand to thereafter output the measured strain magnitude as an outputsignal which can be used to calculate the force component magnitude andhence the applied load.

[0013] The load sensor itself can be used in a variety of applications.As can be appreciated from the above discussion and the followingdetailed description, the load sensor of the present invention has manycommercially advantageous applications for measuring belt tension insystems driven by an endless belt. The load sensor of the presentinvention may also be used to measure friction between an oscillatingshaft and a bushing as disclosed hereinbelow. It is to be understoodthat the load sensor of the present invention may be applied to a widevariety of measuring applications and not only to those specificallydisclosed in the present application.

[0014] Other objects, features, and advantages of the present inventionwill become apparent from the following detailed description, theaccompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a front plan view illustrating a hub load sensorembodying the principles of the present invention being utilized inconjunction with an idler pulley assembly to measure belt load force;

[0016]FIG. 2 illustrates a gauge ring used in the hub load sensor of thepresent invention;

[0017]FIG. 3 is a sectional view of the gauge ring along line 3-3 ofFIG. 2;

[0018]FIG. 4 is a sectional view of the gauge ring along line 4-4 ofFIG. 3;

[0019]FIG. 5 is a sectional view of the idler pulley assembly along line5-5 of FIG. 1;

[0020]FIG. 6 is a partial sectional view of the idler pulley assemblyalong line 6-6 of FIG. 1;

[0021]FIG. 7 illustrates a circuit board used in the hub load sensor;

[0022]FIG. 8 illustrates a schematic diagram of the circuitry of thecircuit board and a pair of strain gauges;

[0023]FIG. 9 is a sectional view of the hub load sensor being utilizedto measure the frictional forces between a bushing and an oscillatingshaft;

[0024]FIG. 10 is a sectional view along line 10-10 of FIG. 9;

[0025]FIG. 11 illustrates the hub load sensor being utilized at an anglein an idler pulley assembly to measure belt tension;

[0026]FIG. 12 is a sectional view of the hub load sensor being utilizedwith a slip ring device in a torque transmitting pulley assembly tomeasure belt tension;

[0027]FIG. 13 is a sectional view along line 13-13 of FIG. 12;

[0028]FIG. 14 is a sectional view along line 14-14 of FIG. 10;

[0029]FIG. 15 shows an alternative pulley assembly arrangement with thegauge ring spaced axially from the pulley member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

[0030]FIG. 1 illustrates a hub load sensor, generally indicated at 10,fixedly mounted on a non-rotatable shaft 12 and being utilized inconjunction with an idler pulley assembly 14 to measure the belt loadapplied by a belt 16 operatively associated with the idler pulleyassembly 14. The tension in the belt 16 applies a force in a loadmeasuring direction indicated by arrow V on the idler pulley assembly14. As will be seen from the following description, the hub load sensor10 is designed to measure forces in the load measuring direction shownin FIG. 1 as vertical. It is not necessary to orient the hub load sensorin a vertical direction to accomplish the objects of the presentinvention. By measuring forces in the load measuring direction, the hubload sensor 10 can be utilized to determine the tension in belt 16.

[0031] The hub load sensor 10 comprises two general components: a gaugering 18 and a strain measuring and outputting device in the form of astrain gauge circuitry assembly 20. The gauge ring 18 is made ofhardened steel and has a generally cylindrical exterior shape. Referringto FIGS. 2, 3, and 4, a cylindrical bore 22 concentric with the axis ofrotation for the pulley assembly 14 extends through the gauge ring 18and defines an interior surface 24 of the gauge ring 18 for receiving astationary shaft such as, for example, shaft 12 of the pulley assembly14. Two semicircular concave indentations or grooves 26 are defined onthe interior surface 24 of the gauge ring 18 opposite one another andextend through the gauge ring 18 parallel to the axis of pulleyrotation. The semi-circular grooves 26 are designed to engagesemicircular projections on a shaft, such as those indicated at 28 onshaft 12 in FIG. 1, thereby fixedly mounting the hub load sensor 10 onthe shaft and preventing rotation of the ring 18 during dynamicconditions as will be described.

[0032] The gauge ring 18 has an upper flat cavity 30 and a lower flatcavity 32 disposed on opposite sides of the gauge ring 18. The flatcavities 30,32 extend through the gauge ring 18 in a direction parallelto the axis of pulley rotation. Also, the flat cavities 30,32 have awidth in a transverse direction perpendicular to the load measuringdirection. The width of each flat cavity 30,32 is significantly greaterthan the height and extends symmetrically with respect to the loadmeasuring direction. Each flat cavity 30,32 is created by the wireelectronic discharge machining method (wire EDM). In the wire EDMmethod, the gauge ring 18 is immersed in non-conductive liquid, such asoil, and an electrically charged wire is used to cut through the ring18. This method is particularly useful for cutting through hardenedsteel. Holes 34 are formed axially through the gauge ring 18 prior tothe wire EDM process, either by drilling or by conventional EDM method,to allow the charged wires to be fed through the hardened steel gaugering 18 to create the flat cavities 30,32.

[0033] The gauge ring 18 also has two upper arcuate cavities 36,38extending axially through the gauge ring 18 parallel to the axis ofpulley rotation. The upper arcuate cavities 36,38 are disposedsymmetrically in the gauge ring 18 with respect to a bisecting linewhich extends in the load measuring direction and divides the gauge ring18 into semi-cylindrical portions. Each upper arcuate cavity 36, 38 hasan upper flat portion 36 a,38 a, an arcuate portion 36 b,38 b, and alower flat portion 36 c,38 c. Each upper flat portion 36 a, 38 a isdisposed parallel to and spaced generally radially inwardly from theupper flat cavity 30. The region of the gauge ring 18 between the upperflat cavity 30 and upper flat portions 36 a,38 a of the upper arcuatecavities 36,38 defines a pair of transversely extending upper flexingbeam members 40 a and 40 b which have a generally rectangular plateconfiguration and will be discussed in detail below.

[0034] Each arcuate portion 36 b,38 b is formed in the shape of an arcgenerally concentric to the axis of pulley rotation and extendsgenerally downward from the upper flat portions 36 a,38 a to or close toan imaginary transversely extending bisecting line which isperpendicular to the aforementioned imaginary bisecting line extendingin the load measuring direction and also divides the gauge ring 18 intotwo semi-cylindrical portions. The lower flat portions 36 c,38 c extenddownward from the arcuate portions 36 b,38 b in the load measuringdirection. The flat portions 36 c,38 c extend lengthwise in the loadmeasuring direction generally parallel to one another and perpendicularto flat portions 36 a,38 a. The upper arcuate cavities 36,38 also havegenerally triangular cavity portions 36 d,38 d at the juncture of thearcuate portions 36 b,38 b and the upper flat cavities 36 a,38 a. Likethe upper and lower flat cavities 30,32, the upper arcuate cavities36,38 are also created by a combination of predrilled holes through thetriangular cavity portions 36 d, 38 d and wire EDM.

[0035] Additionally, the gauge ring 18 also has two lower arcuatecavities 42,44 extending axially through the gauge ring 18 parallel tothe axis of pulley rotation. The lower arcuate cavities 42,44 aredisposed symmetrically in the gauge ring 18 with respect to theaforementioned imaginary bisecting line extending in the load measuringdirection. Each lower arcuate cavity has a lower flat region 42 a,44 a,an arcuate region 42 b,44 b generally concentric with respect to theaxis of pulley rotation, and an upper flat region 42 c,44 c. Each lowerflat region 42 a,44 a is disposed parallel to and spaced generallyradially inwardly from the lower flat cavity 32. The region of the gaugering 18 between the lower flat cavity 32 and the lower flat regions 42a,44 a of the lower arcuate cavities 42,44 defines a pair oftransversely extending lower flexing beam members 46 a and 46 b whichhave a generally rectangular plate configuration and will be discussedin detail below.

[0036] Each arcuate region 42 b,44 b is formed in the shape of an arcgenerally concentric with the axis of rotation and extending upward fromthe lower flat regions 42 a,44 a. The upper flat regions 42 c,44 cextend upward from the arcuate regions 42 b,44 b in the load measuringdirection and are disposed parallel to and spaced generally radiallyinwardly from the lower flat portions 36 c,38 c of the upper arcuatecavities 36,38. Two generally triangular regions 42 e,44 e are formed atthe juncture of the upper flat regions 42 c,44 c and the arcuate regions42 b,44 b.

[0037] Generally inwardly facing interior surfaces of the upper flatregions 42 c,44 c and generally inwardly facing interior surfaces of thegenerally triangular regions 42 e,44 e are formed continuously to definestrain gauge mounting surfaces 52,54. The strain gauge mounting surfaces52,54 extend in the load measuring direction parallel one another. Theregions of the gauge ring 18 between the strain gauge mounting surfaces52,54 and the lower flat cavities 36 c,38 c define plate-like strainablebeam members 48,50.

[0038] The lower arcuate cavities 42,44 also have generally triangularcavities 42 d,44 d at the juncture of the arcuate regions 42 b,44 b andthe lower flat regions 42 a,44 a. Like the upper and lower flat cavities30,32 and the upper arcuate cavities 36,38, the lower arcuate cavities42,44 are also created by the wire EDM method as discussed above.

[0039] Together the upper and lower arcuate cavities 36,38,42,44 dividethe gauge ring 18 into an inner gauge ring portion 56 and an outer gaugering portion 58. Reliefs 60,62 are cut out of the inner gauge ringportion 56 and expose the strain gauge mounting surfaces 52,54 such thatthese surfaces 52,54 communicate with the cylindrical bore 22. The innergauge ring portion 56 and the outer gauge ring portion 58 are integrallyconnected only by the plate-like transversely extending upper and lowerflexing beam members 40 a,40 b,46 a, 46 b and the plate-like strainablebeam members 48,50 extending in the load measuring direction.

[0040] The plate-like configuration of the upper and lower flexing beammembers 40 a,40 b,46 a,46 b allow these members to be flexible in theload measuring direction and very stiff in the transverse direction.Application of a load in the load measuring direction to the exterior ofthe gauge ring creates slight relative movement between the outer gaugering portion 58 and the inner gauge ring portion 56, which is fixedlymounted to the stationary shaft 12. Application of a load having forcecomponents in both the load measuring and transverse directions willmove the ring portion 58 in accordance with the load measuring andtransverse force components. The flexibility of the upper and lowerflexing beam members 40 a, 40 b,46 a, 46 b in the load measuringdirection allows the outer gauge ring portion 58 to move in the loadmeasuring direction with respect to the inner gauge ring portion 56. Thestiffness in the transverse direction of the upper and lower flexingbeam members 40 a,40 b,46 a,46 b, however, minimizes and substantiallyprevents movement of the outer gauge ring portion 58 in the transversedirection with respect to the inner gauge ring portion 56.

[0041] The plate-like strain members 48,50 are long and relatively thinand extend in the load measuring direction connecting the outer gaugering portion 58 to the inner gauge ring portion 56. These strain members48,50 are subject to very low bending stresses in the transversedirection due to the stiffness of the flexing beam members 40 a,40 b,46a,46 b in the transverse direction. The relative movement permitted bythe upper and lower flexing beam members 40 a, 40 b,46 a, 46 b of theouter gauge ring portion 58 with respect to the inner gauge ring portion56 creates strain in the strain members 48,50 in the load measuringdirection. By permitting relative movement of the outer gauge ringportion 58 with respect to the stationary inner gauge ring portion 56and minimizing transverse relative movement of the outer gauge ringportion 58, relative movement is substantially isolated to the loadmeasuring direction and produces strain in the strainable beam members48,50 in the load measuring direction only. Strain gauges 106,110oriented in the load measuring direction and strain gauges 108,112oriented in the axial direction of the strain gauge circuitry assembly20, which will be discussed in detail below, are mounted on the exposedregions 64,66 of the strain gauge mounting surfaces 52,54 to measure thestrain in the strainable beam members 48,50.

[0042] Additionally, the gauge ring 18 has three mounting holes68,70,72, best shown in FIGS. 2-4, configured to receive mounting pins74,78,76, respectively, shown in FIG. 1. The mounting pins 74,76,78 arepreferably made of copper. Retaining holes 82,84,86 corresponding to themounting holes 68,70,72 are formed in a circuit board 80 of the straingauge assembly 20 which is best shown in FIG. 7. The mounting pins74,76,78 are inserted through the retaining holes 82,84,86, soldered tothe circuit board 80, and then inserted into the mounting holes68,70,72. The mounting pins 74,76,78 are secured in the gauge ring 18 bya bonding material 88, thus mounting the circuit board 80 to the gaugering 18. The bonding material 88 is preferably solder, epoxy glue, orother similar bonding substance.

[0043] Printed circuitry 89, best shown in FIG. 7, is printed on theface of the circuit board 80. The printed circuitry 89 is preferablymade of copper. Also, the circuit board has a terminal block 93 on whichfour terminals 95 are located. The technology used to produce circuitboard 80 is well known in the art.

[0044] The strain gauge circuitry assembly 20 comprises the circuitboard 80, the two strain gauges 106,110 oriented in the load measuringdirection, the two axially oriented strain gauges 108,112, and a cableassembly 116. One load oriented strain gauge 106 and one axiallyoriented strain gauge 108 are fastened to the strain gauge mountingsurface 52. The other load oriented strain gauge 110 and the otheraxially oriented strain gauge 112 are fastened to the strain gaugemounting surface 54. These strain gauges are commercially available andwell known in the art. It is preferred that the strain gauges mounted toeach surface 52,54 are disposed on the same matrix backing material 105.The strain gauges 106,108,110,112 are fastened by applying an adhesiveto the matrix backing materials 105 and adhering them to associatedsurfaces 52,54. Strain gauge adhesives are well known in the art andcommercially available.

[0045] Although it is possible to measure the load in the using only theload oriented strain gauges 106,110 it is preferred to use both the loadoriented strain gauges 106,110 and the axially oriented strain gauges108,112. The axially oriented strain gauges 108,112 reduce errors due tothe shift of the load in an axial direction with respect to thecylindrical exterior surface 19 of the gauge ring 18, misalignment ofthe matrix backing materials 105, and the thermal behavior of the hubload sensor 10 including all structural steel parts and all componentsof the strain gauge circuitry assembly 20.

[0046] The plurality of connecting wires 114 connect the strain gauges106,108,110,112 to the circuitry 89 on the circuit board 80. FIG. 8 is aschematic diagram illustrating these connections and the referencenumerals in the strain gauge circuitry assembly 20 correspond to thesame reference numerals in FIG. 8. The schematic diagram of FIG. 8depicts what is known in the art as a Wheatstone bridge circuit 125. Thecircuit board 80 and printed circuitry 89 is not essential to thepresent invention, but they are preferred over more complex and spaceconsuming wiring.

[0047] Referring more particularly to FIGS. 1, 7, and 8 connecting wire114 a connects axially oriented strain gauge 112 to node D of theprinted circuitry 89. Connecting wire 114 b connects the load orientedstrain gauge 110 and the axially oriented strain gauge 112 to node E onthe printed circuitry 89. Node F is connected to the load orientedstrain gauge 110 by connecting wire 114 c. The load oriented straingauge 106 is connected to node C by connecting wire 114 d and to node Bby connecting wire 114 e. Connecting wire 114 e also connects theaxially oriented strain gauge 108 to node B. The axially oriented straingauge 108 is connected to node A by connecting wire 114 f.

[0048] Printed circuit 90 connects node F to node (F) and printedcircuit 94 connects node A to node (A). Both printed circuit 90 andprinted circuit 94 have the same length to ensure that they have thesame resistance. Nodes C and (C) are connected by printed circuit 98.Printed circuit 102 connects node (D) to node D and has the same lengthas printed circuit 98 such that each printed circuit 98,102 has the sameresistance.

[0049] Node (−S) can be connected either. to node (A) or to node (F)with a solder jumper bridge 118 and 120 respectively. Similarly node(+S) can be connected either to node (C) or to node (D) with a solderjumper bridge 124 and 122 respectively. Only one of the jumper bridges118, 120 and one of the jumper bridges 122, 124 are activated during thefinal circuitry calibration. Printed circuit 92 connects node (−S) withnode −S and printed circuit 100 connects node (+S) with node +S. Node Eis connected to node +E by printed circuit 104 and node B is connectedto node −E by printed circuit 96.

[0050] Thin jumper wires 126 are soldered to terminals 95 and theaforementioned nodes. Specifically, a thin jumper wire 126 connectsterminal −E to node −E. Terminal −S is connected to node −S by a thinjumper wire 126. Node +E is connected to terminal +E by a thin jumperwire 126. Another thin jumper wire 126 connects terminal +S to node +S.The thin jumper wires 126 are designed to easily break off of theterminals 95 and the circuit board 80 if the cable assembly 116 and theterminal block 93 are ripped off of the circuit board 80 by accident,thereby preventing damage to the circuit board 80 and the strain gauges106,108,110,112.

[0051] Lead wires 128 are soldered to the terminals 95 and extendthrough the cable assembly 116 to an output device (not shown) and aninput device (not shown). The cable assembly 116 comprises a shrink tube130 and the previously described mounting pin 78. The mounting pin 78extends outwardly from the circuit board 80 and transitions into aplurality of loops, including two in-line loops 132,134 and one offsetloop 136, as best seen in FIG. 6. The preferred triple loop design ofthe long pin with two sections of the pin will allow a secure but gentlemounting of the cable 116 in either direction. This strong but gentlefixing of the cable is especially important in measurement applicationswhere the gauge/pulley/sprocket assembly is installed onto a movingengine component, such as a belt/chain tensioner arm. The lead wires 128pass through the shrink tube 130 in a braided arrangement 138 as bestseen in FIGS. 1 and 5. The shrink tube 130, with the lead wires 128therein, is inserted through the two in-line loops 132,134, folded backupon itself, and inserted through the offset loop 136 as seen in FIG. 6.

[0052] The input device is connected to the lead wires 128 that areconnected to terminals +E and −E and transmits a constant voltage inputto the strain gauge circuitry assembly 20. Although, it is also known inthe art to use a constant current input rather than a constant voltageinput, it is preferable to use a constant voltage input. The outputdevice is connected to the lead wires 128 that are connected to terminal+S and −S. The output device is a voltmeter for reading an outputvoltage across terminals +S and −S. Because the changes in the outputvoltage may be small, an amplifier is usually used in conjunction withthe voltmeter.

[0053] As conditions remain constant, the resistance of the strain gaugecircuitry assembly 20 remains constant and, accordingly, the outputvoltage across terminals −S and +S remains constant. As discussed above,when a force is applied to the hub load sensor 10, the outer gauge ringportion 58 moves in the load measuring direction relative to the innergauge ring portion 56, thereby stretching and creating strain in thestrainable members 48,50 in the load measuring direction. The straingauges 106,108,110,112 mounted on the surfaces 52,54 of the strainmembers 48,50 are therefore also stretched and their resistances changeaccordingly. These changes in resistance results in a change in theoutput voltage across terminals +S and −S which is transmitted to theoutput device.

[0054] Thus, it can be seen that the change in voltage across terminals−S and +S is directly related to the change in the strain in thestrainable beam members 48,50. As discussed above, the strain in thestrainable beam members 48,50 is a direct result of a force applied tothe hub load sensor 10. Accordingly, by properly calibrating the outputdevice and the strain gauge circuitry assembly 20 under controlledconditions with known forces applied to the hub load sensor 10, a force(such as a belt load force) applied to the hub load sensor 10 can bedetermined as a function of the change in output voltage acrossterminals −S and +S.

[0055] As best seen in FIGS. 1 and 8, a thermal compensation wire 117connects node (C) to node (D). The use of a thermal compensation wire117 in a Wheatstone bridge circuit 125 is well known in the art. Thethermal compensation wire 117 is preferably made of copper and minimizesthe change in resistance of the other wires in the strain gaugecircuitry 20 due to temperature changes. A bridge balance wire 119connects node (A) to node (F). The use of a bridge balance wire 119 inthe Wheatstone bridge circuit 125 is also well known in the art.Preferably, the bridge balance wire 119 is made of manganin. The bridgebalance wire 119 balances out inequalities in the Wheatstone bridgecircuit 125 due to differences in length in the other wires in thestrain gauge circuitry 20.

[0056] As shown in FIG. 1, the hub load sensor 10 can be used in theidler pulley assembly 14 to measure the tension in the belt 16. The hubload sensor 10 is fixedly mounted on the non-rotatable shaft 12 as shownin FIG. 1. As best shown in FIG. 5, inner lock rings 140 are press-fitaround the hub load sensor 10 on the outer surface 19 of the gauge ring18. One or more low profile ball bearing assemblies 142 shown in FIG. 5are disposed between the inner lock rings 140 and fit on to the exteriorsurface 19 of the gauge ring 18. Two outer lock rings 144 are snuglyfitted inside a pulley member 146 which is adhered to the outer race ofthe ball bearing assembly 142 such that the ball bearing assembly 142 isdisposed between the two outer lock rings. The belt 16 engages with theouter surface 148 of the pulley member 146 as shown in FIG. 1.

[0057] The use of the lock rings has four advantages:

[0058] 1) ball bearing slide/light press fit will not adversely affectbearing radial clearances even in elevated temperatures,

[0059] 2) ball bearing slide/light press fit will not adversely affectgauge readings even in elevated temperature,

[0060] 3) two gauge lock rings can be made in diametrically matchingpairs to guarantee an even press fit loading on the gauge ring, and

[0061] 4) gauge lock rings protect ball bearing seals and also givewider mounting support surface for the printed circuit board.

[0062] Tension in the belt 16 results in a force in the load measuringdirection V on the pulley assembly. This vertical force is transmittedthrough the pulley member 146 to the ball bearing 142 and to the gaugering 18. As discussed above, forces applied to the gauge ring 18 resultin strain in the strainable beam members 48,50 which in turn causes achange in the output voltage across terminals −S and +S directly relatedto the magnitude of the strain. By previously calibrating the outputdevice and the strain gauge circuitry assembly 20, the belt tension canbe measured as a function of the change in the output voltage acrossterminals −S and +S (and hence strain magnitude) that results from theforce applied to the gauge ring 18 in the load measuring direction bythe belt 16.

[0063] A computing device (not shown) in the form of a microprocessor ora similar device may be connected to the strain gauge circuitry 20. Thecomputing device can be adapted to calculate the force magnitude as afunction of the measured strain magnitude.

[0064] It is to be understood that the hub load sensor 10 is not belimited to the use of measuring belt tension in an idler pulley assembly14 and that other uses of the hub load sensor 10 of the presentinvention are contemplated. For example, utilizing the same principles,the hub load sensor 10 could be used to measure the tension in a chainin a chain and sprocket assembly simply by substituting a sprocket forthe pulley member 146 and the chain for the belt 16. Similarly the hubload sensor 10 can be used to measure tension in anynon-load-transmitting continuously running element passing over a rotaryelement which is adapted to receive the hub load sensor 10. Such runningelements may include paper web, thin wires or textile threads. It isgenerally possible to make both the force bearing strain members 48, 50and the upper and lower flexing members 40 a, 40 b and 46 a, 46 b thinenough to keep the sensitivity of the unit high enough. However, in caseof very low hub loads it may be desirable to reduce the width of theabove mentioned elements (40 a, 40 b, and 46 a, 46 b) by removing somematerial from their outer edges can be appreciated from thecross-sectional view of FIG. 14, taken through the line 14-14 in FIG.10. Also, FIGS. 9 and 10, for example, illustrate the hub load sensor 10being used to measure the coefficient of friction between a bushing 150and an oscillating shaft 152.

[0065] The oscillating shaft 152 is driven by an oscillating motor 154.The bushing 150 fits around the oscillating shaft 152 and is preventedfrom rotating with the shaft 152 by being press-fit to a non-rotatablebushing support 156 disposed around the bushing 150. The cylindricalinner surface 24 of the gauge ring 18 fits in fixed relation on thebushing support 156 to mount the hub load sensor 10 on the bushingsupport. The hub load sensor 10 is mounted in non-rotatable relationrelative to bushing support 156 as a result of cylindrical nodes 158engaging the semi-circular concave grooves 26 in the gauge ring 18 andsemi-circular concave grooves 159 on the bushing support 156. Thebushing 150 does not rotate in relation to the bushing support 156 orthe hub load sensor 10. The hub load sensor 10, the bushing support 156,and the bushing 150 are supported by a sensor stand 160 with the hubload sensor 10 held in a sensor mounting block 161. The sensor mountingblock 161 is connected to the sensor stand 160 via sliding mechanism 175which allows the sensor mounting block to move in the direction of loadL. The oscillating shaft 152 is rotatably supported by shaft stands 162.

[0066] In this friction-detecting arrangement, the load sensor 10 isrotated by 90 degrees in comparison with the environment in FIG. 1. As aresult, when a vertical force is applied in direction L, as shown inFIGS. 9 and 10, the force is transmitted to the inner ring portion 56without a significant amount of strain being seen by the strainablemembers 48,50 due the stiffness of the flexing beam members 40 a, 40b,46 a,46 b due to the fact that the hub load sensor 10 and its mountingblock 161 can slide vertically downwards. The force in the direction Lcauses friction between the bushing 150 and the oscillating shaft 152 asthe shaft 152 oscillates as indicated by arrow 164 in FIG. 10. Thefriction between the bushing and the shaft is seen as a force component(see arrow 166) tangential to the oscillating shaft 152 in the loadmeasuring direction of the gauge ring 18. The friction force istransmitted through the bushing support 156 to the load sensor 10,thereby applying forces in the load measuring direction to the innergauge ring portion 56 of the load sensor 10. The directions of thefriction force at the interface of the bushing support and the gaugering 18 is indicated by arrows 166 in FIG. 10.

[0067] The forces in the load measuring direction on the inner gaugering portion 56 cause the inner gauge ring portion 56 to move withrelative to the outer gauge ring portion 58. Similar to the movementsdescribed with regard to the environment depicted in FIG. 1, themovement of the inner gauge ring portion 56 relative to the outer gaugering portion 58 is substantially isolated to the load measuringdirection by the flexing beam members 40 a,40 b,46 a,46 b and the strainmembers 48,50 are stretched and compressed as the shaft 152 oscillatesback and forth and applies force to the inner gauge ring portion 56.This stretching and compressing is seen as a strain by the strain gauges106,108,110,112 and is directly related to the change in the outputvoltage across terminals −S and +S which is transmitted to the outputdevice. Because the strain in the strain members 48,50 is directlyrelated to the friction between the oscillating shaft 152 and thebushing 150, the friction can be determined as a function of the changein the output voltage across the terminals −S and +S. Furthermore, thecoefficient of friction between the bushing 150 and the oscillatingshaft 152 can be determined as a function of the force applied in thedirection L and the friction between the bushing 150 and the oscillatingshaft 152 as measured by the change in voltage.

[0068] The present invention is not limited to measuring loads orfriction in the transverse or load measuring direction with respect tothe hub load sensor 10. A load on the load sensor 10 at an angle α tothe load measuring direction is shown in FIG. 11. This load has a forcecomponent in the load measuring direction having a magnitudeapproximately equal to the load multiplied by cosα. Thus, load on thehub load sensor 10 at a given angle α can be determined by dividing theload measured in the load measuring direction by the hub load sensor 10by cosα.

[0069] Furthermore, the load sensor 10 is not limited to measuring loadsin a stationary manner. It is contemplated that the hub load sensor 10can be mounted on rotating members in addition to the previouslydiscussed stationary members. For example, FIGS. 12 and 13 illustratethe hub load sensor 10 being utilized in a torque transmitting pulleyassembly 168 to measure tension in a belt 170 operatively associatedwith the torque transmitting or driven pulley assembly 168.

[0070]FIG. 12 is a sectional view of the hub load sensor 10 beingutilized in the torque transmitting pulley assembly 168. The hub loadsensor 10 is fixed to the torque transmitting shaft 172 so that itrotates with the shaft 172. The semi-circular grooves 26 on the gaugering 18 and semi-circular grooves 184 on the shaft 172 engage circularrods 182. Inner lock rings 140 discussed above are press-fit over thehub load sensor 10. A pulley member 190 fits tightly over the inner lockrings 140 and has a portion extending radially inwardly which fitsbetween the inner lock rings 140 and contacts the exterior cylindricalsurface 19 of the gauge ring 18. The outer surface 191 of the pulleymember 190 is engaged with the belt 170. A slip ring device 174operatively connects the lead wires 128 to the input device (not shown)and the output device (not shown). Slip ring devices are well known inthe art for allowing an electric signal to be transmitted from a movingpart to a stationary part and vice versa.

[0071] The slip ring device 174 comprises a slip ring mounting assembly176 with a plurality of slip ring disks 178 and stationary slip ringshoe conductors 180. The slip ring mounting assembly 176 is mounted tothe shaft 172 by a bolt 186 inserted into a bore 188 in the shaft 172.Four slip ring discs 178 are disposed around the slip ring mountingassembly 176 and secured thereon by a slip ring cap 179. The slip ringdisks 178 are insulated from the bolt 186 and from each other by a layerof insulation sleeve 192 and insulation discs 193. The lead wires 128are each connected to corresponding slip ring disks 178.

[0072] These slip ring disks 178 rotate with the shaft 172 and the hubload sensor 10 and maintain constant contact with the stationary slipring shoe conductors 180. The slip ring shoe conductors 180 are heldstationary by a shoe conductor retainer 194. The shoe conductor retainer194 comprises two members 195,197 which hold the shoe conductors 180stationary between two layers of electric insulating material 196. Thetwo members 195,197 are held together by a bolt 200.

[0073] The slip ring shoe conductors 130 transmit signals through wires198 from the input device to the corresponding terminals 95 and from thecorresponding terminals 95 to the output device. Thus, the strain gaugecircuitry 20 of the hub load sensor 10 is operatively connected to theinput and output devices and allowed to rotate with the torquetransmitting pulley assembly 168. Accordingly, the tension in the belt170 can be determined while the torque transmitting pulley assembly 168is rotating. Using the cosine relation discussed above, the tension inthe belt 170 can be determined at any given time when the angle withrespect to the load measuring direction at which the hub load sensor 10is rotated is known. Voltage input and output transmitting devices otherthan the slip ring device 174, such as a device that transmits signalsby telemetry, may be used to transmit input and output signals from therotating hub load sensor 10 for stationary input and output devices.

[0074]FIG. 15 shows an alternative pulley assembly arrangement formeasuring belt tension. The gauge ring 18 is fixedly mounted in ahousing 200. The shaft 202 may be rotatably mounted or fixedly mounted.The shaft 202 in FIG. 15 is rotatably mounted and the pulley member 204is mounted directly to the shaft 202 with no ball bearing assemblytherebetween. In a fixed shaft arrangement, the pulley member 16 wouldbe mounted on a ball bearing assembly. As before, a belt 206 is engagedwith the pulley member 204. A ball bearing assembly 208 fits within thegauge ring 18 and the shaft 202 is mounted inside the ball bearingassembly 208 for rotational movement. A load applied by the belt 206deflects the shaft 202 and causes the inner ring portion of the gaugering to move relative to the outer ring portion in the manner describedabove with respect to the other embodiments, thereby providing a loadmeasurement.

[0075] In summary, to measure hub load as close to the belt/pulleyinterface possible, the load sensing strain gauge in the gauge ring isseparated from the belt only by the low profile ball bearing and thepulley ring mounted over this ball bearing. Due to the close proximityof the belt/pulley interface and the load measuring strain gauges, evena slight variation in the belt tension is immediately sensed by thestrain gauges. Thus, dynamic hub load is accurately measuredcontinuously.

[0076] Because of the long, relatively thin strain gauged load bearingsections of the gauge ring, the offset of the hub load does not affectthe readings of the gauges located at the centerline of the device.Thus, the device is insensitive to belt mistracking.

[0077] Due to the fact that the load bearing (strain gauged) sections ofthe gauge ring are thin, the strain gauges are sensitive enough forhighly accurate readings. However, since the structure is in tension,the stretch of the measuring sections—relative movement between innerand outer ring section—stays very short. Consequently, the moving mass(the outer ring section, low profile ball bearing and pulley ring) isalso quite small resulting in the natural frequency of the device itselfbeing high and well above operational frequencies of any standard beltdrive system under measurement exercise. Thus, the device is sensitive,but rigid enough so that it does not change the natural frequencies ofthe drive system and does not allow its own inertia to affect the loadreadings.

[0078] Finally, due to the location of strain gauges inside the closedpockets of the gauge ring, it is virtually impossible to damage thegauges except by overheating and/or over loading the device. The overloading can further be prevented by the narrow gap between the inner andouter ring sections of the gauge ring, which closes under theoverloading conditions removing the load carrying functions from thestrain gauged sections. The reliability of the wiring, on the otherhand, has been achieved by using the above-mentioned printed circuitboard design.

[0079] It is to be understood that the foregoing embodiments areprovided to illustrate the functional and structural principles of thepresent invention and are not intended to be limiting. Any modificationsor alterations may be made to the above embodiments within the scope ofthe appended claims.

[0080] It should be noted that claim language in the “means or step forperforming a specified function” format specified by 35 U.S.C. § 112,paragraph 6, has been omitted from the appended claims. This is toclearly point out that the claims are not intended to be interpretedunder § 112, paragraph 6, so as to be limited solely to the structuresdisclosed and their equivalents.

What is claimed is:
 1. A load sensor comprising: an annular gauge ringcomprising an annular inner ring portion and an annular outer ringportion; said gauge ring having strainable beam members extending in aload measuring direction and flexing beam members extending in atransverse direction generally perpendicular to said load measuringdirection, said strainable and said flexing beam members interconnectingsaid inner and outer ring portions; said flexing beam members beingthicker in comparison to said strainable beam members so that saidflexing beam members are less subject to elongation and compression dueto strain in comparison to said strainable beam members such that saidflexing beam members substantially limit relative movement between saidring portions to said load measuring direction when a load with a forcecomponent in said load measuring direction is applied to one of saidring portions by (1) resisting elongation and compression tosubstantially prevent relative movement between said ring portions insaid transverse direction and (2) flexing to allow limited relativemovement between said ring portions in said load measuring direction;said strainable beam members being constructed and arranged such thatthe substantially limited relative movement between said ring portionscreates a strain in said load measuring direction in said strainablebeam members having a magnitude directly related to a magnitude of theforce component in said load measuring direction; a strain measuring andoutputting device operatively associated with said strainable beammembers, said strain measuring and outputting device being operable tomeasure the magnitude of the strain created in said strainable beammembers and to thereafter output the measured strain magnitude as anoutput signal which can be used to calculate the magnitude of theaforesaid force component and hence the applied load.
 2. The load sensorof claim 1, further comprising a computing device operatively connectedto said measuring and outputting device, said computing device beingadapted to calculate the force component magnitude and hence the appliedload as a function of the measured strain magnitude.
 3. The load sensorof claim 1, wherein said gauge ring has a first pair of arcuate cavitiesarranged symmetrically with respect to said load measuring direction anda second pair of arcuate cavities arranged symmetrically with respect tosaid load measuring direction; said arcuate cavities extending axiallythrough said gauge ring and cooperating to define said inner ringportion and said outer ring portion.
 4. The load sensor of claim 3,wherein each of said first and second arcuate cavities has an arcuateportion and a substantially straight portion extending in said loadmeasuring direction, the substantially straight portion of each of saidfirst arcuate cavities being arranged adjacent and generally parallel tothe substantially straight portion of an associated one of said secondarcuate cavities so as to define said strainable beam memberstherebetween.
 5. The load sensor of claim 4, wherein said gauge furthercomprises a pair of substantially straight cavities arranged generallysymmetrically with respect to and extending generally in said transversedirection; each of said first and second arcuate cavities having anothersubstantially straight portion extending generally in said transversedirection; the another substantially straight portion of each of saidfirst arcuate cavities being arranged adjacent and generally parallel toone of said substantially straight cavities so as to define one of saidflexing beam members therebetween; the another substantially straightportion of each of said second arcuate cavities being arranged adjacentand generally parallel to the other of said substantially straightcavities so as to define the other of said flexing beam memberstherebetween.
 6. The load sensor of claim 5, wherein said gauge ring ismade of hardened steel.
 7. The load sensor of claim 6, wherein saidcavities are formed by wire EDM.
 8. The load sensor of claim 5, whereinsaid strainable beam members each have interiorly facing strain gaugemounting surfaces extending generally in said load measuring direction;said strain measuring and outputting device comprising strain gaugesoriented in said load measuring direction adhered to said strain gaugemounting surfaces.
 9. The load sensor of claim 8, wherein said strainmeasuring and outputting device further comprises strain gauges orientedin the axial direction adhered to said strain gauge mounting surfaces.10. The load sensor of claim 8, wherein said strain measuring andoutputting device comprises a printed circuit board connected to saidstrain gauges.
 11. The load sensor of claim 8, wherein said strainmeasuring and outputting device comprises a voltage measuring device anda constant voltage supply and said printed circuit board has printedcircuitry cooperating with said strain gauges to define a Wheatstonebridge circuit comprising: a pair of input nodes connected to saidconstant voltage supply; a pair of output nodes connected to saidvoltage measuring device, one of said output nodes being in series withthe strain gauge of one of said strain gauge mounting surfaces and theother of said output nodes being in series with the strain gauge of theother of said strain gauge mounting surfaces; said series being inparallel and connected to each of said input nodes; said voltagemeasuring device measuring a voltage output across said output nodeswhich can be used to calculate the magnitude of the aforesaid forcecomponent of the applied load.
 12. A pulley assembly for measuringdriving element tension in a system driven by a tensioned endlessdriving element, said pulley assembly comprising: a rotatable pulleymember having a driving element engaging outer surface engageable withthe tensioned driving element such that the driving element applies aload to said pulley member directly related to the driving elementtension, the load having a force component in a load measuringdirection; a shaft, said pulley member being mounted to said shaft; anda load sensor comprising: an annular gauge ring comprising an annularinner ring portion and an annular outer ring portion; said gauge ringbeing operatively associated with one of said pulley member and saidshaft such that the load applied to said pulley member causes relativemovement between said ring portions; said gauge ring having strainablebeam members extending in said load measuring direction and flexing beammembers extending in a transverse direction generally perpendicular tosaid load measuring direction, said strainable beam members and saidflexing beam members interconnecting said inner and outer ring portions;said flexing beam members being thicker in comparison to said strainablebeam members so that said flexing beam members are less subject toelongation and compression due to strain in comparison to saidstrainable beam members such that said flexing beam memberssubstantially limit relative movement between said ring portions to saidload measuring direction when the tensioned driving element applies theaforesaid load with the force component in said load measuring directionto said pulley member by (1) resisting elongation and compression tosubstantially prevent relative movement between said ring portions insaid transverse direction and (2) flexing to allow limited relativemovement between said ring portions in said load measuring direction;said strainable beam members being constructed and arranged such thatthe substantially limited relative movement between said ring portionscreates a strain in said load measuring direction in said strainablebeam members having a magnitude directly related to a magnitude of theforce component in said load measuring direction; a strain measuring andoutputting device operatively associated with said strainable beammembers, said strain measuring and outputting device being adapted tomeasure the magnitude of the strain created in said strainable beammembers and to thereafter output the measured strain magnitude as anoutput signal which can be used to calculate magnitude of the aforesaidforce component and hence the driving element tension.
 13. The pulleyassembly of claim 12, further comprising a computing device operativelyconnected to said measuring and outputting device, said computing devicebeing adapted to calculate the force component magnitude and hence thedriving element tension as a function of the measured strain magnitude.14. The pulley assembly of claim 12, wherein said gauge ring has a firstpair of arcuate cavities arranged symmetrically with respect to saidload measuring direction and a second pair of arcuate cavities arrangedsymmetrically with respect to said load measuring direction; saidarcuate cavities extending axially through said gauge ring andcooperating to define said inner ring portion and said outer ringportion.
 15. The pulley assembly of claim 14, wherein each of said firstand second arcuate cavities has an arcuate portion and a substantiallystraight portion extending in said load measuring direction, thesubstantially straight portion of each of said first arcuate cavitiesbeing arranged adjacent and generally parallel to the substantiallystraight portion of an associated one of said second arcuate cavities soas to define said strainable beam members therebetween.
 16. The pulleyassembly of claim 15, wherein said gauge further comprises a pair ofsubstantially straight cavities arranged generally symmetrically withrespect to and extending generally in said transverse direction; each ofsaid first and second arcuate cavities having another substantiallystraight portion extending generally in said transverse direction; theanother substantially straight portion of each of said first arcuatecavities being arranged adjacent and generally parallel to one of saidsubstantially straight cavities so as to define one of said flexing beammembers therebetween; the another substantially straight portion of eachof said second arcuate cavities being arranged adjacent and generallyparallel to the other of said substantially straight cavities so as todefine the other of said flexing beam members therebetween.
 17. Thepulley assembly of claim 16, wherein said gauge ring is made of hardenedsteel.
 18. The pulley assembly of claim 17, wherein said cavities areformed by wire EDM.
 19. The pulley assembly of claim 16, wherein saidstrainable beam members each have interiorly facing strain gaugemounting surfaces extending generally in said load measuring direction;said strain measuring and outputting device comprising strain gaugesoriented in said load measuring direction adhered to said strain gaugemounting surfaces.
 20. The pulley assembly of claim 19, wherein saidstrain measuring and outputting device further comprises strain gaugesoriented in the axial direction adhered to said strain gauge mountingsurfaces.
 21. The pulley assembly of claim 19, wherein said strainmeasuring and outputting device comprises a printed circuit boardconnected to said strain gauges.
 22. The pulley assembly of claim 20,wherein said strain measuring and outputting device comprises a voltagemeasuring device and a constant voltage supply and said printed circuitboard has printed circuitry cooperating with said strain gauges todefine a Wheatstone bridge circuit comprising: a pair of input nodesconnected to said constant voltage supply; a pair of output nodesconnected to said voltage measuring device, one of said output nodesbeing in series with the strain gauge of one of said strain gaugemounting surfaces and the other of said output nodes being in serieswith the strain gauge of the other of said strain gauge mountingsurfaces; said series being in parallel and connected to each of saidinput nodes; said voltage measuring device measuring a voltage outputacross said output nodes which can be used to calculate the magnitude ofthe aforesaid force component of the applied load.
 23. The pulleyassembly of claim 12, wherein said inner ring portion of said annulargauge ring has a mounting bore formed therethrough, said gauge ringbeing fixedly mounted to said shaft by inserting said shaft into saidmounting bore, said pulley member being rotatably mounted to an exteriorsurface of said gauge ring.
 24. The pulley assembly of claim 23, whereinthe surface defining said mounting bore and said shaft cooperate toprevent relative rotational movement between said shaft and said gaugering.
 25. The pulley assembly of claim 24, further comprising a rod,each of said shaft and the surface defining said mounting bore having acooperating indentation, said rod being inserted between said shaft andthe surface defining said mounting bore so as to be received in saidindentations and prevent relative rotational movement between said shaftand said gauge ring.
 26. The pulley assembly of claim 24, furthercomprising a ball bearing assembly, said ball bearing assembly beingmounted on said exterior surface of said gauge ring and pulley memberbeing mounted to said ball bearing assembly for rotational movement. 27.The pulley assembly of claim 12, wherein said shaft is rotatable, saidinner ring portion of said gauge ring having a mounting bore formedtherethrough, said gauge ring being fixedly mounted to said shaft byinserting said shaft into said mounting bore, said pulley member beingfixedly mounted to an exterior cylindrical surface of said gauge ringsuch that said pulley member, said gauge ring, and said shaft rotatetogether. gauge mounting surfaces and the other of said output nodesbeing in series with the strain gauge of the other of said strain gaugemounting surfaces; said series being in parallel and connected to eachof said input nodes; said strain measuring and outputting device furthercomprising a voltage input and output transmitter mounted for rotationalong with said gauge ring; said voltage input and output transmitterbeing connected to said input and output nodes and in continuouscommunication with both said stationary voltage measuring device andsaid constant voltage supply such that said input nodes are continuouslyconnected to said constant voltage supply and said output nodes arecontinuously connected to said voltage measuring device, therebyenabling said voltage measuring device to measure a voltage outputacross said output nodes which can be used to calculate the aforesaidforce component magnitude and hence the driving element tension.
 32. Thepulley assembly of claim 31, wherein said output transmitter is aplurality of slip ring discs mounted for rotational movement along withsaid gauge ring and wherein said stationary voltage measuring deviceincludes a plurality of stationary slip ring conductors, said slip ringdiscs being connected to said input and output nodes and said conductorsbeing continuously engaged with said discs during rotation thereof. 33.The pulley assembly of claim 12, wherein said inner ring portion of saidannular gauge ring has a mounting bore formed therethrough, said pulleymember being mounted to said shaft, said gauge ring being mounted tosaid shaft by inserting said shaft into said mounting bore, said gaugering being spaced axially from said pulley member.
 34. The pulleyassembly of claim 33, wherein said shaft is rotatable and said assemblyfurther comprises a ball bearing assembly mounted inside said mountingbore, said ball bearing assembly having a bore formed therethrough intowhich said shaft is received.
 35. The pulley assembly of claim 34,further comprising a housing constructed and arranged to fixedly mountsaid gauge ring.